Biochips wherein nucleic acids or proteins are immobilized on the surface of a planar substrate include those produced by: the Affymetrix method in which oligonucleotides are synthesized on the surface of a substrate by using photolithography; and the Stanford method in which probe nucleic acids or probe proteins which are prepared in advance are spotted and immobilized on the surface of the substrate. It is well-known that with either type of biochips, fluorescence is detected after a biochemical reaction with a target, and then identification of molecules or diagnosis based on the change in the intensity thereof or pattern thereof is performed. Among the two methods, the Affymetrix method has a drawback in that it is difficult to immobilize stably or synthesize a long oligonucleotide because the synthesize is performed on the surface of the substrate and the cost is high. In the Stanford method, very small spots of materials such as probe nucleic acids and probe proteins are placed on the surface of the substrate, and a “non-covalent type” polylysine or a “covalent type” amino group, aldehyde group, silano group or epoxy group is provided in order to immobilize molecules to be recognized by adsorption or covalent bond. However, there exists a problem that the non-covalent type has a poor stability and a short storage life, and that the amount of probes immobilized decreases with time.
In the covalent type, the amount of functional groups is not uniform over the plane, and the density of probes is non-uniform, and therefore a uniform SN ratio cannot be obtained. The density of the functional groups is also not sufficient, and not sufficient particularly for the density of the proteins immobilized to achieve a reproducibility. Further, the amount of biological substances, particularly proteins, which are non-specifically adsorbed is large, and thus the S/N ratio decreases. Therefore, a substrate which satisfies both of the detection sensitivity and reproducibility cannot be obtained.